ruh roh... another intermittent ignition puzzle, TCI type

Ok, I have been searching for, then reading, every freekin' thread I can find about the TCI ignition....

I have a 1980 "special" that has been torn down to the frame and is being modified to be a Vermont Back Roads Runner.... I have a tci ignition. Wiring harness has been modified and hacked (by me, and I consider myself to be an above-average electrical guy)to the extent that everything actually works to include neutral light, high beams, tail light/turn signals, brake lights etc....this was a bike that had sat for umpteen years without being started or run

Problem is this: bike has been started and run up and down the street, to the tune of 3 or so miles on the odometer! When it runs, it runs great, but when it won't start, well..... ( got it going enough to sort out the idle jets, new mix needles, idles and starts (or, it DID) like a champ)

I have a spark plug tester, the kind that goes inline with the ht plug leads. I bought it cuz I had trouble starting initially, and suspected a weird go/no-go problem with my ignition. I thought I had it all sorted out, but now it has reared its lovely head again. Simply no spark while cranking, or kicking.

The easiest and most fool-proof way to test a TCI is to swap it for a KNOWN good TCI.
You can also try this manual:http://s1100.beta.photobucket.com/user/xscafe/library/manuals/ign manual
It's a pretty good trouble shooting guide made by Yamaha. It goes through a 4-cylinder trouble-shoot, but if you are an above average electrical guy as you say, then you should be able to figure it out. A couple of the wire colors in the guide are different, it helps if you have a color-coded wiring diagram of your year.

Kill and ignition are fine: it would not turn over with either of them nfg... the brakerl light comes on, neutral light comes on, everything works except that there is NO SPARK. Guess I will have to chase down some parts and swap em out to try... tci unit and coil, just to be sure....

Thanks, gggGary.... my gut is telling me that there is no timing signal, since I can get voltage at both wires at the coil... I remember reading somewhere about the pickup magnet and how the alternator magnetism can drown it out (the charging system works fine, as well as everything else....)

All the kill switch does is stop juice from going to the coil. It will not stop the engine from kicking over and the lights would still come on. If the kill is dirty then the coil gets no power. Little things like to crawl into that control. But if you are getting 12v at the coil, then it should be functioning properly.

Thanks for the above... but my comment re: the kill switch: it DOES cut off the start button, both on my XS650 and my BMW R80ST. Per my posts above, there is voltage at the "hot" connection on the coil, and all other functions work when the kill switch is "on". ....and I have cleaned, re-cleaned, plugged and re-plugged every connector. There is something intermittent and I am suspecting the TCI box.

I just found a couple of threads on opening up the TCI and re-soldering old , cracked, cold-soldered joints, so I will be looking into that as well.

Yes, all grounds are good. Replaced the fusebox with an ATC fuse assortment with three fuses and a master fuse as well. Continuity and grounds are no problem.

Per suggestions above, I did two things this evening: first, I disconnected the regulator system to see if it was interfering with the TCI magnetic pickup.... no dice, no difference, no spark.

Second, I pulled the TCI box and opened it up for a visual inspection for cracked solder joints, obvious burns, etc... it all looked amazing and surprisingly good... checked continuity from the 6-gang plug to each of the solder entries into the TCI, all was good...

So, all those quick tests were ok, no detectible problems. Next step is to get a known-good TCI box, since I suspect that is somehow the problem.

I amended above post to include ohming out the pickup coils they should show about 650 -700 ohms from gray to black and orange to black. The wiring that goes through the sprocket area is also prone to breaks and shorts. Tough environment there.

Inspecting the solder joints in the TCI takes a fine eye and a strong magnifier. Look for a circular shadow around where the lead pokes through, or a circular crack about the diameter of the hole where the lead pokes through. They look like they would still be making good contact, but they are bad enough to stop the TCI. Most frequent symptom is the bike will stop for no reason - but - you can immediately start it again. Also as gary mentioned, the pickup can go bad. I had one go bad, one side open. The symptom of that was random spark and backfire and would not start.

On the TCI I'm using, after doing the repair I took it off again and re-soldered every joint in case other cracks were developing. I removed the clear coating on the solder side of the board (don't remember how) and soldered them all, then went over it with a toothbrush and denatured alcohol to remove the rosin. Use the thinnest rosin core solder you can find and add only a touch of solder. It should be the 60% tin, %40 lead, rosin core kind. I meant to put a coating back on but never got around to it. It works fine in any environment still, though. But I could have gotten by just soldering the visibly cracked ones and just soldering through the coating. There were only three or four bad ones visible.

P.S. Might have removed the clear coating the same way I removed the rosin. I think so.

The easiest and most fool-proof way to test a TCI is to swap it for a KNOWN good TCI.
You can also try this manual:http://s1100.beta.photobucket.com/user/xscafe/library/manuals/ign manual
It's a pretty good trouble shooting guide made by Yamaha. It goes through a 4-cylinder trouble-shoot, but if you are an above average electrical guy as you say, then you should be able to figure it out. A couple of the wire colors in the guide are different, it helps if you have a color-coded wiring diagram of your year.

Cool. I've posted that link a couple of times in different threads. It's good to finally know that someone has found it useful.

Make a note on page 87: For 1980-81 XS650s the pick-up coil resistance should be 550-850 ohms. For a 1982 it should be 630-770 ohms. What you're really checking for is that you don't have an open (infinity ohms) or a short (zero ohms).